1. Field of the Invention
The present invention relates to an onboard fuel separation apparatus for an automobile and, more specifically, to an onboard fuel separation apparatus having a separation membrane that separates a material fuel into a high-octane fuel and a low-octane fuel.
2. Description of the Related Art
A technology for separating a material fuel (a fuel used as a raw material) into two kinds of fuels having properties different from the material fuel by using a separation membrane is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-312115. According to the '115 publication, the gasoline in a gasoline tank is separated into a low-boiling point fuel (a fuel having a low boiling point) and a high-boiling point fuel (a fuel having a high-boiling point) by using a pervaporation separation membrane, and the low-boiling point fuel is stored in a fuel tank and is fed to the engine at the start of the engine or during the cold operation. According to the apparatus in '115 publication, the low-boiling point fuel separated from the material fuel during the operation of the engine is used for starting the engine or for the cold operation to improve starting performance of the engine and to improve the emission during the cold operation.
As the low-boiling point fuel is separated from an ordinary gasoline in the apparatus of the '115 publication, the startup performance and the exhaust gas property of the engine in the cold operation can be improved by using low-boiling point fuel without requiring a separate supply of the low-boiling point fuel.
According to the apparatus in '115 publication, however, no consideration has been given to the possibility that the material fuel is not normally separated into the low-boiling point fuel and the high-boiling point fuel, i.e., the occurrence of an abnormal condition in the apparatus has not at all been taken into consideration.
For example, in separating the material fuel by utilizing the pervaporation separation membrane as in the above apparatus, if the separation membrane becomes defective by being damaged, the material fuel passes through the separation membrane without being separated. Therefore, a difference in the boiling point becomes narrow between the low-boiling point fuel and the high-boiling point fuel, and the engine starting performance and the emission during the cold operation are not improved despite of using the low-boiling point fuel obtained by separation.
Though, in the foregoing, a separation apparatus for separating the low-boiling point fuel was described, it becomes difficult to maintain desired octane values of the high-octane fuel and of the low-octane fuel if the separation membrane becomes defective in the fuel separating apparatus that separates the material fuel into the high-octane fuel and the low-octane fuel by using the separation membrane. Therefore, it becomes difficult to obtain a desired engine performance during the high-load operation of the engine using the high-octane fuel, at the start of the engine using the low-octane fuel, or during a cold operation.